A vehicle body upper structure of that type includes left and right side bodies and a roof front rail joined to the side bodies. The front rail extends laterally and has opposing ends joined to roof side rails of the side bodies. Within each of the roof side rails to which the opposing ends of the front rail are joined, a stay is disposed vertically to increase a strength of the roof side rail, such that a force with which a roof panel is pressed against the roof side rail in performing a single-sided spot welding can be transmitted to the stay, as taught in patent literature 1 below.
The vehicle body upper structure has T-shaped intersections where the laterally extending front rail is joined at its opposing ends to the roof side rails. These intersections make a great contribution to the vehicle body rigidity affecting a NV (noise and vibration) performance of the vehicle body or protection of a passenger compartment (cabin) during roll-over of the vehicle. Recently, it is desired to enhance rigidity and strength of such intersections.
The stay of the vehicle body upper structure of patent literature 1, which is adapted to receive and deliver the pressing force of the roof panel exerted on the roof side rail in performing the single-side spot welding, contributes to the improvement in the NV performance or protection of the cabin during the roll-over of the vehicle. Meanwhile, the intersections of the vehicle body upper structure need to have a higher strength. To increase the strength of the intersections, it is thought that the front rail is required to be thick. However, when the thick front rail is joined to the roof side rail by single-sided spot welding, an insufficient weld penetration is formed in the thick front rail. As a result, the weld strength between the thick front rail and the roof side rail is undesirably low.